Conventionally, water dispensers have been used primarily in offices and in hospitals. With a growing interest in water safety and health in recent years, however, water dispensers are gaining popularity among ordinary households. A well-known type of water dispenser is one in which a replaceable raw water container is set in a housing, and drinking water filled in the raw water container is allowed to fall by gravity into a cold water tank housed inside the housing, or the drinking water is pumped up by a pump, as disclosed in the below-identified Patent Documents 1 and 2.
In the above mentioned water dispenser, a raw water supply passage which allows communication between the raw water container and the cold water tank includes a joint portion configured to be detachably connected to a water outlet port of the raw water container. The raw water container including a cap is generally used. As the cap, one including an inner tube protruding into the interior of the raw water container and defining a water outlet port of the raw water container, and a plug closing the water outlet port, is used. The plug includes a bottomed cylindrical portion configured to be fitted to the inner tube of the cap with its opening facing the exterior of the raw water container. The joint portion, which is configured to be inserted into this cap, comprises a cylindrical member including a straight portion configured to be fitted to the inner tube of the cap, a tip portion configured to be fitted inside the bottomed cylindrical portion of the plug so that the plug is stably engaged with the tip portion. The joint portion is connected to the water outlet port by being inserted into the inner tube of the cap. The tip portion of the joint portion inserted into the inner tube of the cap is pressed against the bottomed cylindrical portion of the plug, so that the tip portion is fitted inside the bottomed cylindrical portion, and the plug is stably engaged with the tip portion so as not to be disconnected from the joint portion. Once the plug is stably engaged with the tip portion, and then the plug is disconnected from the inner tube of the cap. Since the tip portion will be covered by the bottomed cylindrical portion when the tip portion is fitted therein, a water flow hole, through which raw water in the raw water container can be supplied into the joint portion, cannot be formed in the tip portion. Therefore, the water flow hole is formed in the straight portion of the joint portion and configured to open to the interior of the raw water container at a position away from the inner tube of the cap. As described above, when the joint portion is inserted into the raw water container to reach a position where the entire water flow hole opens to the interior of the raw water container, the straight portion of the joint portion is fitted to the inner tube of the cap with an interference fit. Due to the straight portion of the joint portion being brought into a close contact with the inner tube of the cap over the entire circumference thereof, a sealing effect to prevent the leaking of water from inside the raw water container can be obtained (for example, in water dispensers disclosed in below-identified Patent Documents 3 and 4).
Among these, a water dispenser is known in which, as shown in FIGS. 11(a) and (b), the inner peripheral surface of an inner tube 101 of a cap 100 is provided with a stepped portion 102 having a smaller diameter at its portion closer to the interior of the raw water container, and a fastening belt portion 103 formed contiguous to the stepped portion 102 on the smaller diameter side thereof. In this water dispenser, a fitting surface 105 is formed on the outer peripheral surface of the bottomed cylindrical portion of the plug 104, and configured to be fitted to the fastening belt portion 103 with an interference fit. The fitting between the fitting surface 105 and the fastening belt portion 103 provides a sealing effect to the raw water container before use. An engaging portion 106 is formed on the outer peripheral surface of the bottomed cylindrical portion and configured to engage with the stepped portion 102. During the transportation of a raw water container, the engagement between the engaging portion 106 and the stepped portion 102 prevents the plug 104 from being disconnected from the inner tube toward the interior of the raw water container. A guiding cylindrical portion 107 formed contiguous to the stepped portion 102 on the larger diameter side thereof guides the outer periphery of the a joint portion 108 such that the misalignment of the center of the joint portion 108 and the center of the inner tube 101 is controlled within a predetermined range. When the joint portion 108 is inserted into the raw water container such that an entire water flow hole 109 opens to the interior of the raw water container, as shown in FIG. 11(a), a sealing effect can be provided due to a straight portion 110 being brought into close contact with the fastening belt portion 103 over the entire circumference thereof. At this time, the straight portion 110 faces the guiding cylindrical portion 107. The straight portion 110 is not configured to be fitted to the guiding cylindrical portion 107 with an interference fit. If the straight portion 110 is configured to be fitted to the guiding cylindrical portion 107 with an interference fit, the guiding cylindrical portion 107 could be pushed inappropriately by the straight portion 110 in the radial direction of the inner tube, due to various errors, which in turn causes the fastening belt portion 103 to move away from the straight portion 110, possibly resulting in a loosening of the close contact between the fastening belt portion 103 and the straight portion 110 over the entire circumference thereof. As a result, the straight portion 110 may not be properly inserted into the inner tube 101 at the initial stage of the insertion process, and an insertion failure is more likely to occur.